28-41-02
 QUANTITY INDICATORS  ú ú 02.1 Page 8 ú Jul 12/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 C.  AIRPLANES WITH THE OPEN TUBE TYPE OF FUEL MEASURING STICK (DRIPSTICKS); To operate the fuel measuring stick, apply a slight pressure and turn the fuel measuring stick 90 degrees in the counterclockwise direction. Slowly lower the fuel measuring stick until fuel appears from the drip hole (Fig. 3). Read the fuel quantity on the fuel measuring stick to find the quantity of fuel in the fuel tank.
 D.  AIRPLANES WITH THE MAGNETIC FLOAT TYPE OF FUEL MEASURING STICK; To operate the fuel measuring stick, it is unlocked from the base by applying a slight pressure and a 90-degree counterclockwise turn to the end of the stick. When the fuel measuring stick is unlocked, it is lowered to the fully extended position. Depending on fuel level, a bearing found on top of the stick will magnetically latch onto a magnet in the float before full extension. In this event, a slight pressure should be applied to assure a full extension. At the fully extended position, the fuel measuring stick stops against a cushion giving a soft firm feel.
 (1)  
To find the fuel level, the fuel measuring stick is gently raised until the magnetic latch is felt to engage. There is a positive feel in this position since the magnetic latch is strong and will jerk the fuel measuring stick into its position. The fuel measuring stick is now read to find the fuel level in the fuel tank.

 (2)  
If the fuel measuring stick is being monitored during a refuel or defueling operation, the float and stick sub assembly will move with the fuel level. However, since the magnetic attachment between the magnets of the stick sub assembly and float causes a small friction against the housing, the stick sub assembly and float will not move up smoothly with the fuel level, but in distinct jumps as the fuel level rises on the float to overcome the static friction. On declining fuel levels when defueling, friction will occur in the opposite direction. Calibration marks on the stick sub assembly are set to read on rising fuel levels and the most accurate reading will be immediately after a jump of the stick sub assembly.

 9.  Operation (Fig. 2)_________
 A.  The fuel quantity indicating system operates on 115v ac power from the standby bus or external power bus.
 B.  The fuel quantity indicator does a capacitance measurement with a sine wave. The fuel quantity indicator microcomputer feeds a sine wave to the tank units and a sine wave that is 180 degrees out of phase with the tank unit sine wave to the compensator unit. The microcomputer measures the capacitance of the tank units, then measures the capacitance of the compensator unit. With these two values, it calculates and shows the fuel mass.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH SIMMONDS DIGITAL FUEL ú

 28-41-02
 QUANTITY INDICATORS  ú ú 01 Page 9 ú Nov 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
N62 TANK 2 FUELINGN63 CENTER TANK N61 TANK 1 FUELINGIND (P15) FUELING IND (P15)FUELING IND (P15)115V AC
STBY BUSINTERNALS SAMEINTERNALS SAMEINTERNALS SAMEC397 AS N50 AS N50 AS N50
F12
QTY

FUEL SYSTEMS115V ACF10EXT PWR
RECEPTACLE C398 F9
EP GNDR10 FUEL POWERFUELING
F18 P6-3 CIRCUIT BREAKER PANEL
SELECT RELAYF12
(E3-3) F21 F8
F7  F11
F6F10
NO. 2 S160 FUEL IND
F9TANK TEST IND (P15)
F5F21R309 FUEL POWER
TRANSFER RELAYF4 F7 F8
F5 F6POWERSUPPLY
F3
F2
COMP
F4 POWERSUPPLY
M1097 LB/KG SELECT F18F3
TRIMMERCENTER
TANK 2
FUELF2
TANK 2
ZERO AND FULL TANK
QTY
PROC

SCALE ADJUST F11
TANK 1 F14 F16 F2F17
CTR TANK F3 D1586 SELF TEST M290 ADAPTER
BUSSING
FUEL SUMMATION UNIT
ASSY TANK 2
PLUG
N50 TANK 2 FUEL QTY IND F4
F16  F6
F5 F8 F17 F7
INTERNALS
SAME AS

COMP
F14  F21
N50 F9
D1590 NO. 1
F10
BUSSING M291 ADAPTER TANK PLUG ASSY CTR TANK
　
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